Saturday, March 24, 2007

How - To: crankarm lengths

I'm about 5'7" and have short legs. I have something like a 29" inseam. I ride a size Small Giant TCR. As you probably know already, I sprint well, I don't TT or climb well.

Normally sprinting means short cranks. Track racers typically use 165's, and 170's are considered "long". The realm of long cranks are the mysterious and elusive worlds of climbing and TT'ing. Mysterious and elusive to me anyway.

Sprinting. Speed over power. Explosive acceleration. 19,000 rpm Formula 1 versus 1,500 rpm Mac trucks.

But then I look at BMX racers. They race a one speed bike, it's a very low gear, and their races are essentially standing start sprints. But they use the longest cranks possible - it's sort of normal to have 180's. It just seems to go against my intuition. I figure they get a jump at the start then immediately spin out and get passed. But that's not the case. They go like crazy all the way to the line.

In 2001 my fitness deteriorated as I spent a lot of time with my mom. I'd get out to do my favorite Summer Street Sprints, but I was going slower and slower all the time - my speed dropped from about 43 mph to just over 30 mph over the course of the year. My race results reflected this lack of fitness. There were races where I lasted one lap, group rides where I got shelled on the first hill.

In the warm-up.

I was hurting.

Nevertheless, in October 2001, I went for a ride with a not-racing-anymore teammate David (ex Cat3). As unfit as I was, he claimed to be even less fit. To "handicap" myself, he asked me to ride my mountain bike while he rode his road bike. Unlike my road bikes and my previous mountain bikes, this mountain bike had 175's (my road bikes had 170's). Normally I'd put the same crank length on my mountain bike (so my legs trained on the same crank length), but since this was a beater trade, I left it totally stock except to put on a longer stem. The bike retained its original unusably bent middle ring, the 2 pound steel bead tires, the bent bottle cage, even the seat.

During the ride, my friend struggled on some of the bits where you need some semblance of aerobic fitness. Even on the mountain bike I got antsy. I really wanted to make a big effort so I asked him if he was okay with it. He was, I went, and he dug deep to stay on my wheel. After I eased he came up next to me, excited and thrilled at the burst of speed. I had gone 33 mph on a slight uphill with quite a bit of a cross/head wind.

And I hadn't sprinted per se, I just powered my biggest gear while seated.

My mountain bike had nothing "fast" on it. Compared to my 18 or so pound road bike with 22 mm 120+ psi tires, drop bars, and better gears, I shouldn't have gone as fast "pursuiting" on the mountain bike as sprinting on my road bike.

I thought about those BMX'ers and figured the 175's might be the ticket.

I bought a pair of 175's (same model as my 170's, just longer) and put them on my road bike. If they didn't work out, I'd give them to some taller rider. With my updated bike I went out to my favorite sprint road. My previous sprints were at 31-33 mph. 7 minutes into my ride, I sprinted on the 175's (identical bike otherwise).

41 mph.

The 175's stayed.

No kidding right? I also bought another set for my second bike. And I decided to keep them on the mountain bike.

I've heard a lot of people preach about how long cranks screw up knees. I thought about this too since I didn't want to screw up my very fragile knees. And I came up with the following ideas/steps:

1. When I put the 175's on it was sometime in late Oct, early Nov. I rode them on a trainer and rollers till February, focusing on spinning. My long rides were over two hours long, and one was over three hours. My initial comfortable cadence dropped from 110+ on 170's to below 80 on 175's. For reference, after five years, I've been stable at being comfortable at 95-100 rpms.

2. I dropped my seat about 5 mm so I kept my same leg extension. My knee has more of an acute angle at the top of the pedal stroke but I figured the extension would be more important.

3. The seducing aspect of long cranks is that you can use much bigger gears. Instead of spinning a 39xsomething up a hill, you just pound a 53x15. Anytime you push big gears at lower rpms, you increase the load on your knees (and the length of time of the load). This kills your knees. I was very careful to try and keep my cadence similar to my short crank cadence on climbs (80-ish or more). Realistically I dropped about 10 rpms to 70-ish, but this beats the 50 or 60 that I wanted to do initially.

4. I did a LOT of time on the bike getting used to the cranks. I only started making violent efforts when I felt comfortable with the cranks.

I can say the following:
1. I have yet to have any pain beyond the normal aches during my "training camps" where I ride months of my normal training time in a couple weeks.

2. After not placing at the CT Criterium Championships for a long time, and training less and less from Sept 2000 till July 2002, I placed an extremely close second at the Nutmeg State games and won the CT Criterium Gold Medal. I've since added a silver, a gold, and a bronze. The last time I won a medal was a silver in 1995 (when I was much more fit, about 40 lbs lighter, and I was on 167.5's). This has a flat finish which favors speed.

3. After not placing overall at the Bethel Spring Series (which as you know I promote and race in), I placed second, first, and third overall in the 2004, 2005, 2006. This has an uphill sprint so it favors a longer crank.

4. I still can't TT or climb.

I have found long cranks to be very, very helpful. I previously tried longer (172.5) cranks a few times but gave up after a week or two. I had to commit and get used to the long cranks in order to use them successfully.

If you are careful and sensible, you may find that longer cranks work well for you.

1 comment:

suitcaseofcourage said...

Great analysis. You'd mentioned the shorter cranks in an earlier post, so I thought maybe shorter cranks would be "faster" (like spinning a wheel from near the hub, rather than near the rim - too much geometry for me though), but this post confirms my decision to stay with my stock 172.5s. Thanks again for such great posts.